Silicon-on-sapphire (SOS) has been used for a number of years as a substrate for the fabrication of integrated circuits. The quality of the epitaxial material, as grown, has limited its device utility to special purpose applications such as satellite electronics where its inherent radiation hardness properties are exploited, Techniques for reducing the defect densities of the silicon film have extended the applicability of the material to very advanced, fully depleted, submicron field effect transistors (FETs), These devices have a very large commercial potential.
SOS is commercially produced by atmospheric pressure chemical vapor deposition of silicon on highly polished sapphire substrates, This material is plagued with microtwin defects which cause diffusion spikes, lower mobilities, and junction shorts. The literature teaches that these microtwins can be removed by solid-phase epitaxial (SPE) regrowth of the film, see the article by S. S. Lau et al, entitled "Improvement of Crystalline Quality of Epitaxial Si Layers by Ion-Implantation Techniques," Appl. Phys. Lett. 34(1), 1 Jan. 1979. The technique of this article involves the amorphization of a portion of the film containing the defects by ion implantation with silicon followed by a SPE regrowth. By dramatically reducing the defect density of the silicon/sapphire interfacial region, the material can be utilized in the construction of high performance FETs with submicron gate lengths. By thinning the material down to 1000 .ANG. or below, the FETs can be operated in a fully depleted mode, further enhancing their performance.
In accordance with this inventive concept, therefore, a need has become discovered for a method of using recently developed epitaxial growth techniques which can be applied to produce silicon-on-sapphire films in a more direct fashion to offer potentially more thickness uniformity and control with reduced defect densities.